Abstract: A flow control device comprises an inlet side; an outlet side; and a sealing member between the inlet and the outlet side. A diaphragm selectively opens or closes or control a degree of closure of an opening between the inlet and the outlet sides depending on the proximity of the diaphragm to the sealing member. The diaphragm comprises a first portion of one side of the diaphragm exposed to the inlet side fluid pressure and a second portion of the same side of the diaphragm exposed to the outlet side fluid pressure and the opposite side of the diaphragm exposed to a control fluid pressure. The movement of the diaphragm between the open and closed states is governed by the inlet, outlet and control pressures which cause deformation of the diaphragm.